GABA synchronizes clock cells within the suprachiasmatic circadian clock

The master clock in the suprachiasmatic nuclei (SCN) is composed of multipl e, single-cell circadian clocks. We test the postulate that these individua l "clock cells" can be synchronized to each other by the inhibitory transmi tter gamma-aminobutyric acid (GABA). For these experiments, we monitored th e firing rate rhythm of individual clock cells on fixed multielectrode plat es in culture and tested the effects of GABA. The results show that the dai ly variation in responsiveness of the SCN to phase-shifting agents is manif ested at the level of individual neurons. Moreover, GABA, acting through A- type receptors, can both phase shift and synchronize clock cells. We propos e that GABA is an important synchronizer of SCN neurons in vivo.